I. Field of the Invention
This invention relates generally to the construction of implantable electronic tissue stimulator systems, and more particularly to a design in which a battery power pulse generator, feed-through assembly and lead header are all contained within a metal case.
II. Discussion of the Prior Art
Implantable electronic tissue stimulating devices, such as cardiac rhythm management devices (pacemakers and defibrillators) and a variety of implantable muscle/nerve stimulators conventionally comprise a battery-powered electronic pulse generator contained within a hermetically sealed metal housing or case and attached to the housing or case is a molded polyurethane lead header. The lead header is commonly affixed to the metal case by metal brackets along with a medical grade adhesive. In this regard, reference is made to the Oleen et al. U.S. Pat. No. 5,261,395, assigned to the assignee of the present application. In that patent, a hybrid electronics board along with a battery power source, is contained within the case and affixed to a generally flat top surface thereof is a header 28 in the form of a molded polyurethane biocompatible body 30. The header has a plurality of lead receiving cavities in which are fitted connector blocks 38 and 46. The connector blocks have aligned bore(s) generally concentric with lead receiving bore(s) formed in the polyurethane header whereby electrical stimulating lead(s) having male terminal pins on the proximal end thereof can be inserted. The connector blocks 36 and 46 are, in turn, connected through the connector pins of a feed-through assembly to points on the electronic circuitry contained within the case 26.
While the arrangement described in the Oleen et al. ""395 patent has proven to be highly reliable, it involves a variety of expensive manufacturing processes that necessarily increase the cost of the resulting product. For example, prior to affixing the polyurethane header to the case, it needs to be subjected to a cleaning process, such as plasma cleaning, to remove oil residues leaching out from the polymer to prepare the surface for optimal bond strength. Polyurethane headers may require repeat cleaning if they are not affixed shortly after the cleaning process.
Further, once the polyurethane header is assembled onto the case the adhesive involved is cured and degassed by being subjected to elevated temperatures in an oven for several hours.
Ongoing efforts by the industry to reduce the size of the implantable device have been very successful. Early implantable pacemakers back in the 1960""s were about the size of a hockey puck. With advances in microelectronics and integrated circuitry, significantly more features and capabilities have been embodied in implantable devices, such as pacemakers and defibrillators, capable of sizes as small as about 10 cc. Nonetheless, efforts to further reduce the size of implantable pulse generators continue in the industry.
A need, therefore, exists for an implantable electronic tissue stimulating device that is less expensive to manufacture and whose physical size can be reduced compared to state-of-the-art commercial designs.
The foregoing needs are met in accordance with the invention by providing an implantable tissue stimulating device in which a battery and an electronic circuit powered by the battery, the header assembly, including its connector blocks and feed-through assembly, are all contained within an all-metal case. This result is achieved by providing a metal header housing having a cavity for containing a connector block holder that is formed from an insulating material and which contains at least one electrically conductive lead connector. The connector block holder and lead connector are insertable into the cavity of the header housing through an aperture that leads to the cavity in the header housing. A feed-through assembly, comprising a metal feed-through mounting plate that supports, but is insulated from, at least two conductive pins, is welded into the aperture to thereby hermetically seal the metal header housing from the electronic circuit and battery compartment. One of the two conductive pins connects to a first point on the electronic circuit and to the at least one lead connector while another of the conductive pins connects a second point on the electronic circuit to the metal header housing.
Following this construction, in which all components are contained within a single metal case, the need for medical adhesive and the problems associated with it are obviated. Furthermore, by eliminating a molded polyurethane header, manufacturing cost reductions are realized. The full metal case, where the metal in question is titanium, allows further size reductions and simplifies the creation of a hermetically sealed environment for the electronic circuit and battery. Patients who may have an allergic reaction to medical grade adhesives and/or the polyurethane used for the header material also benefit from the use of a full metal (titanium) case.